This invention relates generally to a medium feed mechanism for a printer and, in particular, to a medium feed mechanism for a so called point-of-sales (POS) printer having a means for transport of a recording medium, such as, a slip sheet or paper, or validation card, through the printer in micro fed steps such as, in increments of less than 1 mm, permitting printing directly to the edges of the recording medium, i.e., printing from the leading edge to the trailing edge of the recording medium.
POS printers are micro printers capable of handling various types of recording medium, such as, a sheet or slip medium, card or validation medium or a rolled medium. They are also referred to as slip printers. The POS market requires that different kinds of recording medium be employed with a single printer as housed in a modern day electronic cash register. However, to incorporate several capabilities into a single slip printer is difficult because of a large number of moving mechanisms required in a single printer to provide for the capability of printing on two or more different kinds of recording media. Further, the bulkiness of the printer structure is large in order to provide for several drive sources in the printer to drive several different transport means positioned along a medium pathway within the printer. U.S. Pat. No. 5,061,095 exemplifies in prior art FIGS. 11 through 14 some of these problems concerning slip printers of the prior art.
U.S. Pat. No. 5,061,095 discloses an improvement over these prior art printers wherein, as shown in FIG. 6(a), a single power source 9 is employed for the printer to operate two pairs of spaced apart, transport rollers 5, 6 and 7, 8 to feed a recording medium 12, such as, a slip sheet, through the printer and past print head 1 for printing. Engagement of respective pressure rollers 6 and 8 in contact with their respective drive rollers 5 and 7 is brought about by operation of the respective solenoids 28 and 18. When the trailing edge of slip medium 12 in the medium pathway has almost passed or has just passed the position of drive roller 7, medium 12 is engaged between rollers 5, 6 for continued incremental feeding past print section 1 so that roller 8 may, therefore, be disengaged from drive roller 7 by release of the plunger of solenoid 18. However, as the trailing edge of slip medium 12 passes from between rollers 5, 6, there is a large bottom portion of slip medium 12 in which no printing can be accomplished because there is no longer any transport rollers in the printer operative for continued engagement of medium 12. The length of medium 12 upon which printing cannot be successfully accomplished is approximately the distance between rollers 5, 6 and the print head 1a of printer section 1. As a result, not all of the slip medium printable surface can be reliably utilized for printing, which is a problem when additional data is desired to printed on the same standardized slip medium or printing is to be accomplished on a nonstandard size slip medium.
Moreover, as the slip medium is transported adjacent to printer section 1, the leading edge of the print medium, at this point, is an unsupported, extended free end so that, while the medium is held in a firm grip by rollers 5, 6, it is still difficult to print on the medium surface while achieving the highest attainable print quality since the extended free end of the medium is not under any direct control of the incremental drive movement applied to the medium. Furthermore, since, at this point, there is only a single pair of rollers 5, 6 directly controlling the transport of the slip medium through the printer, changes in the alignment and transport direction, as well as variances in the particular incremental movement, may occur to the medium as the medium is transported past the print head. Such variances are due, in part, to mechanical idiosyncrasies of the paired rollers 5, 6 and their support mechanism. Thus, the printed indicia on the slip medium may not always be accurately aligned in consecutive rows of printed data.
It is an object of this invention to provide a compact, simple structured medium feed mechanism for a printer capable of transporting a recording medium through the printer section of a printer with incremental feed precision and permitting the printer section to print data on the recording medium starting immediately adjacent to the transported leading edge of the medium and concluding at the immediately adjacent portion to the transported trailing edge so that virtually all of the surface of the medium may be successfully utilized for carrying printed data.
It another object of this invention to provide for accurate control in the transport of a recording medium through a printer by means of selective operation of a series of recording medium transport sections wherein such a transport section is position both at inlet side and the outlet side of the printer section of the printer.
It is a further object of this invention to provide a printer with several transport sections driven in common by a single power source to provide the transport of the recording medium through the printer wherein an operating mechanism at least at one transport section is activated or inactivated by means of operation of operating mechanisms at two other transport sections.